1. Field of the Invention
The present invention relates to control devices operable to be coupled to a communication link, specifically, a method of confirming that a control device, such as a digital electronic ballast, complies with a predefined protocol standard, such as the Digital Addressable Lighting Interface (DALI) standard.
2. Description of the Related Art
Typical load control systems are operable to control the amount of power delivered to an electrical load, such as a lighting load or a motor load, from an alternating-current (AC) power source. Lighting control systems for fluorescent lamps typically comprise a controller and a plurality of electronic dimming ballasts that are operable to communicate via a digital communication link. The controller may communicate with the ballasts using, for example, the industry-standard Digital Addressable Lighting Interface (DALI) communication protocol. The DALI protocol allows each ballast (i.e., each DALI ballast) in the lighting control system to be assigned a unique digital address, to be programmed with configuration information (e.g., preset lighting intensities), and to control a fluorescent lamp in response to commands transmitted across the communication link.
A typical DALI lighting control system includes a link power supply that generates a direct-current (DC) link voltage VLINK (e.g., approximately 18 VDC), which provides power for the DALI communication link. The DALI communication link comprises two conductors (i.e., two wires) and is coupled to each of the ballasts, such that each ballast receives the DC link voltage VLINK of the link power supply. The ballasts are also coupled to the AC power source to receive line voltage (e.g., 120, 240, 277, or 347 VAC) for powering the fluorescent lamps.
According to the DALI protocol, the DALI ballasts encode the digital messages that are transmitted over the communication link using Manchester encoding. FIG. 1 shows an example of a Manchester-encoded digital message 10. With Manchester encoding, the bits of the digital message 10, i.e., either a logic low (or zero) value or a logic high (or one) value, are encoded in the transitions (i.e., the edges) of the message on the communication link. When no messages are being transmitted on the communication link, the link floats high in an idle state. To transmit a logic low (i.e., zero) value, each DALI ballast is operable to “short” the communication link (i.e., electrically connect the two conductors of the link) to cause the communication link to change from the idle state (i.e., approximately 18 VDC) to a shorted state (i.e., a “high-to-low” transition) as shown at time t0 in FIG. 1. Conversely, to transmit a logic high (i.e., one) value, each DALI ballast is operable to cause the communication link to transition from the shorted state to the idle state (i.e., a “low-to-high” transition) as shown at time t1 in FIG. 1. After the final bit, the digital message 10 comprises two stop bits S during which the link is high (i.e., idle) for the length of two full bit times TFB to indicate that the digital message is over.
The transitions of the digital message 10 occur near the middle of consecutive bit windows, which each extend for a full bit time TFB (e.g., approximately 832 μsec) as shown in FIG. 1. Each full bit time TFB consists of two half-bit times THB between the beginning of the full bit time TFB and the transition, and between the transition and the end of the full bit time TFB.
The DALI protocol is standardized in accordance with technical standards published by the International Electrotechnical Commission (IEC), which define many required operating characteristics of DALI ballasts. Specifically, the first revision of the technical standard defining the DALI protocol is IEC standard 60929, while the second revision is IEC standard 62386. The technical standard imposes limitations on the length of the full-bit times TFB and the half-bit times THB of transmitted digital messages. For example, the full-bit times TFB must be between 750 μsec and 916 μsec, while the half-bit times THB must be between 375 μsec and 458 μsec (according to the first revision, i.e., IEC standard 60929). In addition, the IEC standard also defines a maximum value of a delay time TDELAY (or “settling time”) that exists between two consecutively transmitted digital message. For example, the delay time TDELAY may be limited to a maximum of approximately 60 msec. According to the second revision (i.e., IEC standard 62386), the full-bit times TFB must be between 750 μsec and 916 μsec, and the half-bit times THB must be between 334 μsec and 500 μsec.
However, DALI ballasts sold by some manufacturers may not actually operate within the specifications of the DALI standard. If DALI controllers and DALI ballasts from different manufactures are installed on a single DALI communication link and some of the DALI ballasts do not perform within the specifications of the DALI standard, the entire lighting control system may not function correctly as a result. Thus, there is a need for a method of determining if a DALI ballast does not comply to the specifications of the DALI standard.